Gear-type fluid motor or pump

ABSTRACT

This invention relates to a motor or pump of the gear-type including a housing containing a main gear and at least one pinion gear meshing with the main gear. A coupling means drivably engages with the main gear and is drivably engageable with a rotatable member which is driven or driving according to whether the unit is used as a motor or pump. The coupling means is such that the respective rotational axes of the main gear and the driven or driving member may be misaligned during use.

United States Patent Dixon et al.

[451 Jan. 25, 1972 [54] GEAR-TYPE FLUID MOTOR OR PUMP [72] Inventors: Kenneth Raymond Dixon; David Burnett Sugden, both of Kingston Beach, Australia Improved Mechanical Products Pty. Ltd., Tasmania, Australia 22 Filed: on. 18,1968 2| App1.No.: 768,820

[73] Assignee:

[30] Foreign Application Priority Data Oct. 23, 1967 Australia ..28809/67 [52] U.S. Cl ..418/182, 418/196 [51] Int. Cl. ..F0lc 17/00, F0lc 1/08 [58] Field ofSearch ..103/126, 126 BA, 126 D, 126 B, 103/126 L,'125, 126 LB, 126 H; 230/141; 123/12;

[56] References Cited UNITED STATES PATENTS 1,287,118 12/1918 Shore ..103/126B 2,399,008 4/1946 Dora n 103/126 B 2,681,621 6/1954 Hedman ..103/126 8 2,759,426 8/1956 Blomgren et al. 103/126 LB 2,837,031 6/1958 llune ..103/126 H 2,905,095 9/1959 Hartmann eta1.... 103/125 2,955,537 10/1960 Gaubatz 103/126 D 3,090,258 5/1963 Zink et a1 ..74/801 3,128,710 4/1964 Blomgren et al.. ..103/126 LB 3,292,550 12/1966 Gordon ..103/126 H Primary Examiner-Carlton R. Croyle Assistant Examiner-Wilbur J. Goodlin Attorney-Stevens, Davis, Miller & Mosher 5 7] ABSTRACT Claims, 13 Drawing Figures PATENTEU JANZ 51872 SHEET H11" 5 GEAR-TYPE FLUID MOTOR R PUMP This invention relates to a fluid motor or pump of the gear type-that is, of the type utilizing two or more meshing gears which function as the driving or pumping members in a known manner.

Motors or pumps of the above type having a relatively simple construction are generally satisfactory for low-pressure work, but problems have been encountered in designing units suitable for high-pressure applications. For example, highpressure units so far available are usually of extremely complex and/or bulky construction thereby severely limiting their application.

A common construction of motors or pumps of the above type, includes a housing composed of several parts and which encloses the gears in relatively close fitting relationship so as to minimize fluid leakage or slippage between the gears and the adjacent surfaces of those housing parts. In operation however, such motors or pumps are subjected to internal pressures which are unevenly distributed within the housing so that the housing parts which should closely fit the gears tend to deflect away therefrom and allow leakage of fluid under pressure with consequent loss of efficiency.

It is a principal object of the present invention to provide a motor or pump of the above type which is of relatively simple construction and which is suitable for highand low-pressure applications. A further object of the invention is to provide relatively simple means for overcoming the aforementioned deflection without causing any significant increase in the weight or cost of the motor or pump.

The following description refers in more detail to these essential features and further optional features of the invention. To facilitate an understanding of the invention, reference is made to the accompanying drawings where these features are illustrated in preferred form. It is to be understood however, that the essential and optional features of the invention are not limited to the specific forms of these features as shown in the drawings. In the drawings:

FIG. 1 is an end elevational view of one embodiment of the present invention, which view is partially sectioned for convenience of illustration;

FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1;

FIG. 3 is a fragmentary sectional view taken along line III III of FIG. 2;

FIG. 4 is an enlarged sectional view taken along line lV-IV of FIG. I;

FIG. 5 is an enlarged sectional view of a portion of the control valve mechanism shown in FIG. 2;

FIG. 6 is a cross-sectional view taken along line Vl-Vl of FIG. 5;

FIG. 7 is an end view of a further embodiment of the invention, partially sectioned for convenience of illustration;

FIG. 8 is a cross-sectional view taken along line VIllVIII of FIG. 7;

FIG. 9 is an enlarged fragmentary sectional view taken along line lX-IX of FIG. 8, in which view the main gear has been omitted for convenience of illustration;

FIG. 10 is an enlarged cross-sectional view taken along line X-X of FIG. 9;

FIG. 11 is a fragmentary sectional view of a modified version of the embodiment shown in FIG 8;

FIG. 12 is a fragmentary sectional view of a further modification of the embodiment shown in FIG. 8; and

FIG. 13 is a cross-sectional view of yet another embodiment of the invention.

In the particular example shown in FIGS. I to 6, the housing includes an intermediate housing part 2 and two end housing parts 3 and 4. The intermediate part 2 has formed therethrough a major bore 6 which contains a main gear 7 in closely fitting relationship, and one or more minor bores 8 located laterally of the bore 6 but communicating therewith. Preferably, four minor bores 8 are provided in equally spaced relationship about the circumference of the major bore 6. Each minor bore 8 contains a pinion gear 9 in closely fitting relationship, and the lateral spacing of the respective axes of the main gear 7 and each pinion gear 9 is such that the main gear 7 meshes with each pinion gear 9 in a known manner.

The housing end parts 3 and 4 are releasably secured by bolts 11 to opposite ends respectively of the intermediate housing part 2 so as to extend across at least portion of each of the bores 6 and 8 and thereby limit axial movement of the gears 7 and 9 relative to the housing. For best results, such axial movement, or more correctly the end clearance for the gears 7 and 9, should be kept to a minimum. In one form, the gears 7 and 9 each have a length substantially equal to but no greater than the axial thickness of the intermediate housing part 2, and each end housing part 3 and 4 has a planar surface which engages a respective end face of the intermediate housing part 2 and defines an end wall for each of the gear cavities formed by the bores 6 and 8.

Inlet and outlet fluid manifolds l2 and 13 respectively may be provided in the housing end parts 3 and 4 as shown in FIG. 2. Alternatively, the inlet and outlet manifolds l2 and 13 may be fonned in the same housing part 3 or 4. It will be appreciated that although manifolds 12 and 13 may act as inlet and outlet respectively when the unit is used as a motor having a drive in one direction, their roles will be reversed when the direction of drive is reversed. The same may apply when the unit is used as a pump.

Each minor bore 8 communicates with the inlet and outlet manifolds through ports 10 and 15 respectively. In this regard, see FIGS. 1, 3 and 6. Ports 10 are provided in the end part 3, whereas ports 15 are provided in end part 4.

A driving or driven member operatively connected to the main gear 7 may be in the form of a shaft 14 extending through one end of the housing and through an axial bore I6 of the main gear 7, and a quill or hollow shaft 17 may be drivably connected to both the shaft 14 and the main gear 7. Such a drivable connection may include internal and external splines 18 and 19 respectively on the quill 17 which respectively engage with external and internal splines 21 and 22 on the shaft l4 and main gear 7 respectively. The shaft I4 will be driving or driven according to whether the unit is used as a pump or motor respectively.

With the above drive arrangement, each housing end part 3 and 4 is preferably provided with an open ended bore 23 and 24 respectively which are in substantial axial alignment with the bore 16 of the main gear 7. An end cap 26 may be attached over the outer end of the bore 24 and locates within that bore to provide a journal bearing for the adjacent end of the shaft 14. An annular bearing member 27 may be secured to the outer end face of the housing end part 3 to rotatably support portion of the shaft 14 extending through that end part.

In order to avoid or at least minimize distortion of the housing, a pair of compensating members are located one within the other about the intermediate housing part 2. The outer surface of the intermediate housing part 2 is preferably cylindrical in which case the inner compensating member is preferably in the form of a substantially cylindrical band 28. Nevertheless, the outer periphery of that member may have any other appropriate shape, although a cylindrical shape is generally most convenient to form. The internal diameter of the band 28 is predetermined so that it bears against the outer surface of the intermediate housing part 2, and the band 28 preferably extends across the entire width of the outer surface of the intermediate housing part 2.

It is further preferred that the band 28 extends beyond the opposite ends of the intermediate housing part 2 so that end portions of its inner surface bear on cylindrical surfaces 29 and 31 formed on the adjacent end portions of the housing end parts 3 and 4 respectively.

The outer compensating member may be also in the form of a cylindrical band 32, although that is not necessary. It is only necessaRy that the outer member has a bore therethrough which is substantially complementary in cross-sectional shape to the outer peripheral shape of the inner band 28, so as to receive fluid from the inlet manifold bear against the outer surface of that inner band. The outer peripheral shape of the outer member may be of any convenient form.

By way of example, the outer member may constitute a casing for the motor or pump housing which serves as mounting and sealing means as well as fulfilling its primary function as a compensating member. In such an arrangement (not shown), the casing may have a bore therein for receiving the inner band 28 in close fitting relationship, and an end wall defining the aforementioned journal bearing for the adjacent end of the shaft 14. An annular wall may be removably mounted at the other end of the casing to surround the shaft 14 in fluid sealing relationship so that the housing parts 2, 3 and 4 are completely enclosed within the casing. With this particular construction it is not necessary to provide the aforementioned end cap 26 and annular bearing member 27. Also, either one or both of the fluid manifolds may be formed in an end wall of the casing rather than in the housing end parts 3 and 4.

For convenience of description however, the outer compensating member will be hereinafter referred to as the outer band 32.

The outer band 32 preferably extends across substantially the full width of the inner band 28 and engages the outer surface of the inner band 28 at least at the end portions thereof. A fluid chamber 33 is preferably provided between the adjacent surfaces of the bands 28 and 32, and that chamber may be formed by a relatively shallow circumferential groove formed in either or both of those surfaces. Preferably, the groove or chamber 33 is of substantially the same width as the intermediate housing part 2 and is disposed in substantial alignment therewith, for a purpose hereinafter made clear. Also resiiient O-rings or other appropriate sealing means may be provided at or adjacent each side of the groove or chamber 33 to prevent or minimize fluid leakage laterally from the chamber 33 between the two bands 28 and 32.

A fluid supply passage 34 may be formed through the inner band 28 and the intermediate housing part 2 to provide a communication between the fluid manifolds l2 and 13 and the chamber 33. Any appropriate valve mechanism may be employed to control the flow of fluid through the supply passage 34. That is, the valve mechanism may be operable automatically or manually to connect the fluid chamber 33 with a selected one of the manifolds l2 and 13. For example, a shuttle valve 36 may be employed which will automatically connect the fluid chamber 33 to the manifold 12 or 13 which is subjected to the highest fluid pressure, and disconnect the chamber 33 from the manifold subjected to the lower pressure. The valve 36 may connect the chamber 33 to both manifolds l2 and 13 if they are subjected to equal pressures. The shuttle valve 36 is preferably constructed as shown in FlGS. and 6. That is, it is slidably mounted within a lateral passage 37 communicating with passage 34, and has tapered head portions 38 each of which is adapted to close an orifice 39 formed in a respective valve plate 41.

In use, both the compensating fluid chamber 33 and the main fluid chamber defined by the gear cavities, usually 12 so that substantially the same pressure may exist in both chambers. The pressure within the main chamber tends to force the intermediate housing part 2 radially outwardly and is therefore transmitted through that housing part to produce a radially outward thrust against the inner surface of the inner band 28. The pressure within the compensating chamber 33 however, produces a radially inwards thrust against the outer surface of the inner band 28, which inward thrust may be substantially equal to the aforementioned outward thrust because of the substantialiy equal thrust areas involved.

As there is usually a pressure gradient within the main fluid chamber, there will be zones at which the inward thrust on the inner band 28 exceeds the outward thrust thereon. The higher inward thrust however, is usually prevented from causing significant distortion or deflection of the inner band 28 because that band bears on the end housing parts 3 and 4 whichare able to resist relatively high-radial forces because of their relatively large radial thickness.

Similarly, the outward thrust may exceed the inward thrust at some zones, but the resultant outward force is generally insufficient to cause deflection of the inner band 28 such as to disturb the efficiency of the motor or pump. in this regard, the outer band 32 may be of relatively heavy section compared to the inner band 28 thereby providing a solid backing member for the inner band 28.

it will be appreciated from the foregoing that the compensating means described will effectively prevent or reduce deflection or distortion of the housing so that fluid loss due to leakage between the housing and the gears is kept to a minimum over a wide range of pressures. The bulk and weight of a motor or pump utilizing the compensating means described may be considerably less than a motor or pump having a corresponding capacity and which is otherwise rigid enough to resist deflection or distortion by use of previously known means.

A motor or pump incorporating the compensating means described can be pressurized over the outer periphery and end faces of the housing and on the inner surface of the main gear, at a pressure which may be less than the pressure operating the motor or pump, being regulated at some optimum proportion of same. Also, a motor or pump so arranged, having a seal on its driven or driving shaft so that leakage of fluid from areas of high pressure and the compensating chamber 33 to areas of low pressure, will automatically result in a pressure within the compensating chamber 33 which is directly proportional to the system pressure and which may be made to bear on all or selected areas of the housing so as to effectively reduce or prevent deflection thereto.

A further problem encountered with motors or pumps of the type described, is that they are relatively expensive to manufacture because of their complex construction and the tolerances which must be adhered to in order to obtain efficient operation. One particular cause of this problem is the mounting of the gears, and present means for such mounting involves the use of spindles or stub axles for each gear and which are rotatably mounted in appropriate bearings so as to allow the respective gear to turn freely. Such mounting arrangements require that the gears be confined to precise centers of rotation in order that the operating clearance between the gears and the housing can be maintained sufficiently small and consistent so as to minimize leakage of fluid between the gears and the housing.

in addition to the above, such spindles or stub axles and their respective bearings, have been rendered indispensable because of the particular means hitherto adopted for achieving partial balance of the fluid pressure and mechanical loads on the gears. A substantial part of the manufacturing cost of such fluid motors or pumps is incurred in the precise machining operations necessary to locate the spindles or stub axles and bearings within the housing in appropriate relation to the stationary parts of the motor or pump. That location is of course critical so that the respective gears are mounted with suflicient accuracy to achieve the relatively smail working clearances necessary for efficient operation.

The foregoing problem is particularly evident in relation to mounting of the main gear 7. In the construction described, the problem is eleviated by provision of a coupling means for the main gear 7 which allows misalignment of the respective rotational axes of the main gear 7 and the shaft 14. The arrangement is such that the main gear 7 is floatingly mounted within the major bore 6 so that lateral movement of that gear is restricted only by the cylindrical surface of the bore 6. in use however, a film of fluid is formed between the cylindrical surface of the bore 6 and the crown of the teeth of the main gear 7 thereby preventing metal to metal contact between the gear and that surface.

The quill 17 functions as the coupling means and is able to tilt relative to the rotational axis of either the shaft 14 or the gear 7-thereby allowing the aforementioned misaiignment to occur. The splines 18 and 19 of the quill 17 may be manufactured with a backlash to facilitate tilting of the quill axis as required. It will be appreciated that other coupling means such as a Hookes joint or a universal joint may be used with equal effectiveness.

Turning now to the embodiment of FIGS. 7 to 10, that embodiment is of particularly simple construction thereby enabling comparatively economic manufacture and assembly. One of the principal differences between this embodiment and that of FIGS. 1 to 6, is the fact that the housing is constructed in two main parts. The housing parts 103 and 104 abut in a plane extending normal to the rotational axis of the main gear 107, and are retained in assembly by studs 111.

Major and minor bores 106 and 108 communicate as previously described, and in the preferred arrangement there are five minor bores 108. A pinion 109 is provided in each bore 108 so as to mesh with the main gear 107. Each minor bore 108 communicates with inlet and outlet manifolds 112 and 113 through ports 110 and 115 respectively. The manifolds 112 and 113 are both formed in the end part 104, as are the ports 110 and 115 (see FIGS. 8 and 9).

The ports 110 and 115 preferably communicate with the minor bores 108 through respective shallow grooves 151. A narrow channel 152 may be formed at the end of each groove 151 remote from the respective port as shown in FIG. 10. Such channels 152 have been found useful in preventing or minimizing cavitation.

A further important distinction over the previous embodiment is the mounting of the pinion gears 109. As shown in FIG. 8, each minor bore 108 extends completely through the housing parts 103 and 104, although it may extend through only one end face of the housing if desired. The opposite ends of each pinion 109 are secured against relative movement to respective cylindrical bearing members 153. In the embodiment shown, the bearing members 153 are secured to the pinion 109 by screw threads, but any other suitable means may be used. The bearing members 153 are coaxial with the pinion 109 and have the same outer diameter, and the complete pinion assembly is rotatably and slidably located within its respective bore 108.

It will be appreciated that the bores 108 are simple to form, and there is no problem in assembling the pinions 109 within the housing. Each pinion 109 is retained in its correct axial position by teeth of the main gear 107 locating between and being engageable with adjacent faces of the bearing members 153. Seal caps 154 may be removably retained in each end of each bore 108 by circlips 156, or any other appropriate means.

Pressure compensating means may be provided in this embodiment. In one form, such means includes at least one, but preferably two cavities 157 provided in the housing parts 103 and 104 radially outwardly of each minor bore 108. Preferably, each cavity 157 is elongated in the axial direction of the associated pinion 109, and extends for substantially the same length as the pinion 109 and is in substantially radial alignment therewith. Although the cavities 157 may have any suitable shape in transverse cross section, they are preferably arcuate and generally follow the contour of the adjacent bore 108 as shown in FIGS. 7 and 9. A passage 134 (see FIG. 8) connects each cavity 157 with the adjacent bore 108.

The embodiment of FIGS. 7 to 10 also preferably includes a coupling means as described in relation to the previous embodiment. That is, a quill 117 has an outer spline 119 at one end drivably engaging with an inner spline 122 of the main gear 107. An inner spline 118 at the opposite end of the quill 117 engages a spline 121 formed on a shaft 114. The quill 117 and the main gear 107 function as previously described. In particular, the gear 107 is floatingly" mounted.

In a modification of the embodiment of FIGS. 7 to 10, as illustrated in FIG. 11, a shaft 114 is not provided but the quill 117 is arranged to accept the spline for a shaft or any other driving or driven member. Suitable seals 158 and 159 are provided to prevent or minimize fluid leakage. In all other respects, the arrangement is substantially as previously described. Such a construction is particularly applicable to mounting direct on a wheel or a winch for example.

A further modification of the FIGS. 7 to 10 embodiment is illustrated in FIG. 12. In that modification, the compensating means includes a cylindrical band 128 instead of the cavities 157. The band 128 is located within a recess 16], and a fluid receiving space 133 is defined between the inner surface of the band 128 and the base of the recess 161. The inner surface of the band 128 is preferably substantially complementary to the base of the recess so that only a film of fluid is receivable within the space 133. Seals are provided at the corners of the recess 16] to prevent or minimize fluid leakage from the space 133.

The space 133 is connectable with manifolds 112 and 113 through passages 162, 163 and 164. A control valve 136 is preferably provided to automatically connect the space 133 to the manifold subjected to the higher pressure, and to automatically disconnect the space 133 from the manifold subjected to the lower pressure The valve 136 may be of the same basic construction as the valve 36 described in relation to the first embodiment, and consequently has tapered heads 138 operable to close respective orifices 139. Each orifice 139 is connected to a respective one of the passages 163 and 164.

The housing construction and pinion assembly as described in relation to the embodiments of FIGS. 7 to 12, have several important advantages. The housing construction for example is comparatively simple to manufacture and has a high resistance to distortion compared to a three-part housing construction as described in relation to the embodiment of FIGS. 1 to 6. Also, manufacturing errors are necessarily reduced because of the small number of parts comprising the housing. For example, the pinion bores 108 can be formed after the housing parts 103 and 104 are assembled, thereby enabling a high degree of accuracy.

The pinion assembly enables the use of a two-part housing because the bearing members 153 have a common diameter with the pinion body 109. The bearing members 153 carry radial loads applied to the pinion 109 by hydraulic pressure and tooth loads, and they also resist axial hydraulic forces acting between the pinion teeth thereby relieving the housing of those forces. In addition, the members 153 effectively seal the ends of the pinion cavity against loss of fluid and also locate the pinion in its correct axial position by close fitting relationship on opposite sides of the main gear 107. Other advantages of such a pinion assembly will be readily apparent to persons skilled in the art.

Yet another embodiment of the invention is illustrated in FIG. 13. The principal and important distinction of this embodiment is the housing construction. All other components are substantially as described in relation to the first embodiment, and consequently will be given passing reference only.

The housing includes an intermediate part 202 and end parts 203 and 204 which are substantially as described in relation to the first embodiment. Those parts however, are contained within a bore 266 of a casing having a skirt 232 and an end wall 267 which closes one end of the bore 266. Axial movement of the parts 202, 203 and 204 within the bore 266 is restricted by a retainer plate 268 which is releasably locked within the open end of the bore 266 by an annular nut 269.

A plurality of pinions 209 (five for example) are rotatably mounted within the housing and mesh with a main gear 207. Each pinion 209 may have its opposite end portions rotatably mounted in respective end parts 203 and 204 by needle bearings or any other suitable means. A quill 217 drivably connects the main gear 207 to a shaft 214 in the manner previously described so that the main gear 207 is floatingly" mounted. Manifolds 212 and 213 may be provided within the casing end wall 267.

Compensating means is provided and preferably includes a cylindrical band 228 which contains the housing parts 202, 203 and 204 and engages an outer cylindrical surface of each one of those parts. The band 228 is interposed between the aforementioned housing parts and the skirt 232 so that the skirt functions as the outer band 32 of the first embodiment described, and a fluid-receiving space 233 is defined between the band 228 and the skirt 232. The outer surface of the band 228 is preferably substantially complementary to the surface of bore 226 so that only a film of fluid is receivable within the space 233.

Fluid from the major and minor bores (not shown) of the housing is conveyed to the space 233 by passing between the adjacent surfaces of plate 268 and end part 203 and the adjacent surfaces of wall 267 and end part 204. The fluid pressure between those surfaces and in the space 233 is usually substantially the mean of the respective pressures acting in the manifolds 212 and 213. Thus, during use, the housing parts 202, 203 and 204 are completely encapsulated in pressurized fluid thereby minimizing distortion or deflection of those parts.

A shallow groove 271 may be formed in the outer cylindrical surface of the intermediate part 202 so as to allow limited radially inward deflection of the band 228. Preferably, that groove 271 communicates with atmosphere through passages 272, 273 and 274.

It will be appreciated that a casing as described in relation to the last embodiment, may be used with any one of the previous embodiments. Furthermore, the compensating means described in relation to the various embodiments has the important advantage of enabling manufacture of a compact unit in which fine clearances may be provided between the gears and the housing. In particular, the compensating means avoids distortion of the housing such that the pinions foul with their respective surrounding cavity wall.

Having now described our invention, what we claim as new and desire to secure by Letters Patent is:

l. A fluid motor or pump of the gear type including, a housing having a major bore and at least two minor bores formed therein, the axes of the bores being substantially parallel and being relatively disposed so that said bores communicate, a main gear rotatably mounted within said major bore, and arranged so that lateral movement thereof relative to said housing is restricted by a single-bearing surface, said bearing surface being defined by the cylindrical surface of said major bore, a pinion gear rotatably mounted within each said minor bore and meshing with the main gear, a pair of fluid manifolds formed in said housing and respectively communicating with said minor bore, and coupling means drivably connected to said main gear and being drivably connectable to a rotatable driving or driven member, said coupling means allowing misalignment of the respective rotational axes of said main gear and said driving or driven member.

2. A motor or pump according to claim 1, wherein said coupling means includes a quill gear rotatably mounted within said housing, one axial end portion of the quill gear being in driving engagement with said main gear, and the opposite axial end portion being operatively connectable to the driving or driven member.

3. A motor or pump according to claim 2, wherein said quill gear is provided with a set of external teeth and a set of internal teeth, said external and internal sets being spaced apart in the axial direction of the quill gear, said main gear having a set of internal teeth which are substantially complementary to and engage with the external teeth of the quill, and the internal teeth of the quill are engageable with substantially complementary teeth formed on said driving or driven member.

4. A motor or pump according to claim 1, wherein a plurality of said minor bores are provided in equally spaced relationship about the circumference of said major bore, and one of said pinions is located within each of said minor bores.

5, A motor or pump of the gear type including, a housing having a major bore and a minor bore formed therein, the axes of the two bores being substantially parallel and being relatively disposed so that said bores communicate, a main gear rotatably mounted within said major bore, a pinion gear rotatably mounted within said minor bore and meshing with the main gear, a pair of fluid manifolds formed in said housing and respectively communicating with said minor bore,

'coupling means drivably connected to said main gear and surize same and thereby minimize radially outward deflection of the housing part or parts surrounding said bores.

6. A motor or pump according to claim 5, wherein said housing includes an intermediate part defining the cylindrical surfaces of both said bores, and two end parts releasably secured to the intermediate part to form opposite end walls respectively of said bores; and a cylindrical band surrounds and engages a cylindrical outer surface of said intermediate part, the inner surface of said band also engaging a respective cylindrical surface of each of said end parts, an outer compensating member surrounding said band and engaging at least part of the outer cylindrical surface thereof, said compensating means being defined between adjacent cylindrical surfaces of the band and the outer compensating member, and passage means formed within said housing connecting said chamber to at least one of said fluid manifolds.

7. A motor or pump according to claim 6, wherein said passage means is arranged to connect the chamber to both said manifolds, and a valve is provided in said passage means to automatically disconnect the chamber from the manifold which is subjected to the lower fluid pressure and connect the chamber to the manifold which is subjected to the higher fluid pressure.

8. A motor or pump according to claim 5, wherein said coupling means includes a quill gear rotatably mounted within said housing, one axial end portion of the quill gear being in driving engagement with said main gear, and the opposite axial end portion being operatively connectable to the driving or driven member.

9. A motor or pump according to claim 5, wherein a plurality of said minor bores are provided in equally spaced relationship about the circumference of said major bore, and one of said pinions is located within each of said minor bores.

10. A fluid motor or pump of the gear type including, a housing having a major bore and a minor bore formed therein, the axes of the two bores being substantially parallel and being relatively disposed so that said bores communicate, said housing being formed as two parts which are assembled in face to face relationship along a plane extending normal to the axes of said bores and located substantially midway in the axial length of the major bore, said major bore being defined by a pair of complementary pockets each of which is formed in a respective one of said housing parts, said minor bore extending through at least one end face of the housing remote from said plane, a seal cap removably mounted within said minor bore adjacent the or each said end face through which it extends, a main gear rotatably mounted within said major bore, a pinion gear ,rotatablymounted within said minor bore and meshing with the main gear, a cyiindrical bearing member secured to each end of'the pinion gear against movement relative thereto,

each said bearing member having substantially the same outside diameter as said pinion, a pair of fluid manifolds formed in said housing and respectively communicating with said minor bore, and coupling means drivably connected to said main gear and being drivably connectable to a rotatable driving or driven member, said coupling means allowing misalignment of the respective rotational axes of said main gear and said driving or driven member.

11. A motor or pump according to claim 10, wherein said pinion and the associated cylindrical bearing members are rotatably and slidably mounted within saidminor bore, and

said pinion is retained against substantial axial movement by intermeshing teeth of the main gear located between and engageable with adjacent end faces of the bearing members.

12. A motor or pump according to claim 11, wherein said manifolds are formed in the same part of the housing.

13. A motor or pump according to claim 10, wherein said coupling means includes a quill gear rotatably mounted within said housing, one axial end portion of the quill gear being in driving engagement with said main gear, and the opposite axial end portion being operatively connectable to the driving or driven member.

14. A motor or pump according to claim 10, wherein a plurality of said minor bores are provided in equally spaced relationship about the circumference of said major bore, and one of said pinions is located within each of said minor bores.

15. A fluid motor or pump of the gear type including, a housing having a major bore and a minor bore formed therein, the axes of the two bores being substantially parallel and being relatively disposed so that said bores communicate, said housing being formed as two parts which are assembled in face to face relationship along a plane extending normal to the axes of said bores and located substantially midway in the axial length of the major bore, said major bore being defined by a pair of complementary pockets each of which is formed in a respective one of said housing parts, said minor bore extending through at least one end face of the housing remote from said plane, a seal cap removably mounted within said minor bore adjacent the or each said end face through which it extends, a main gear rotatably mounted within said major bore, a pinion gear rotatably mounted within said minor bore and meshing with the main gear, a cylindrical bearing member secured to each end of the pinion gear against movement relative thereto, each said bearing member being coaxial with said pinion and having substantially the same outside diameter as said pinion, a pair of fluid manifolds formed in said housing and respectively communicating with said minor bore, and pressurecompensating means located radially outwards of said minor bore and arranged to minimize radially outward deflection of the housing part or parts surrounding the bores.

16. A motor or pump according to claim 15, wherein said compensating means includes a cavity formed in said housing radially outwardly of said minor bore and communicating therewith through a communication passage.

17. A motor or pump according to claim 16, wherein said cavity is elongated in the axial direction of the pinion, is in substantial radial alignment with said pinion and extends for substantially the full length thereof, and in transverse cross section is shaped as a narrow arcuate groove which generally follows the curvature of said minor bore.

18. A motor or pump according to claim 16, wherein a plurality of said cavities are located side by side adjacent said minor bore.

19. A motor or pump according to claim 16, wherein said pinion and the associated cylindrical bearing members are rotatably and slidably mounted within said minor bore, and said pinion is retained against substantial axial movement by intermeshing teeth of the main gear located between and engageable with adjacent end faces of the bearing members.

20. A motor or pump according to claim 16, wherein said coupling means includes a quill gear rotatably mounted within said housing, one axial end portion of the quill gear being in driving engagement with said main gear, and the opposite axial end portion being operatively connectable to the driving or driven member.

21. A motor or pump according to claim 15, wherein said compensating means includes a cylindrical band at least partially contained within a recess formed in the radially outer surface of the housing, and feed means for feeding fluid under pressure into a space defined between the inner cylindrical surface of said band and the base of said recess.

22. A motor or pump according to claim 21, wherein the inner cylindrical surface of said band and the base of the recesses are substantially complementary so that only a film of fluid is receivable within said space.

23. A motor or pump according to claim 21, wherein said space is communicable with both said manifolds through said feed means, and said feed means includes a valve mechanism operable to automatically communicate the space with the manifold subjected to the higher pressure and prevent communication between the space and the manifold subjected to the lower pressure.

24. A motor or pump according to claim 21, wherein said pinion and the associated cylindrical ,bearing members are rotatably and slidably mounted within said minor bore, and

said pinion is retained against substantial axial movement by intermeshing teeth of the main gear located between and engageable with adjacent end faces of the bearing members.

25. A motor or pump according to claim 15, wherein a plurality of said minor bores are provided in equally spaced relationship about the circumference of said major bore, and one of said pinions is located within each of said minor bores.

26. A motor or pump according to claim 21, wherein coupling means is drivably connected to said main gear and is drivably connectable to a rotatable driving or driven member so as to allow misalignment of the respective rotational axes of said main gear and said driving or driven member said coupling means includes a quill gear rotatably mounted within said housing, one axial end portion of the quill gear being in driving engagement with said main gear, and the opposite axial end portion being operatively connectable to the driving or driven member.

27. A motor or pump according to claim 5, wherein said housing includes, an outer casing having a skirt portiondefining a cylindrical bore and an end wall closing one end of said skirt bore, an intermediate part contained within said skirt bore and defining the cylindrical surfaces of both the major and minor bores, two end parts also contained within said skirt bore and disposed on opposite sides respectively of the intermediate part to form end walls of said major and minor bores, and a retainer plate releasably locked within the open end of the skirt bore so as to restrict axial movement of the housing parts interposed between it and the end wall of the casing.

281A motor or pump according to claim 27, wherein the intermediate and end parts of the housing each has a cylindrical outer surface of substantially the same diameter, and a cylindrical band disposed about said housing parts and engaging the outer cylindrical surfaces thereof, said compensating chamber being defined between the outer cylindrical surface of said band and the adjacent surface of the skirt bore.

29. A motor or pump according to claim 28, wherein the outer cylindrical surface of the band is substantially complementary to the adjacent skirt bore surface so that only a film of fluid is receivable between those surfaces, and fluid is conveyed to said space from the major and minor bores by passing between the adjacent surfaces of said retainer plate and adjacent housing end part and the casing end wall and adjacent housing end part respectively.

30. A motor or pump according to claim 28, wherein the outer cylindrical surface of the intermediate housing part is grooved to allow limited radially inward deflection of said cylindrical band.

31. A motor or pump according to claim 30, wherein said grooved surface of the intermediate housing part communicates with atmosphere.

32. A motor or pump according to claim 27, wherein a plurality of said minor bores are provided in equally spaced relationship about the circumference of said major bore, and one of said pinions is located within each of said minor bores.

33. A motor or pump according to claim 9, wherein lateral movement of said main gear relative to the housing is restricted by a single-bearing surface, and said bearing surface is defined by the cylindrical surface of the major bore.

34. A motor or pump according to claim 14, wherein lateral movement of said main gear relative to the housing is restricted by a single-bearing surface, and said bearing surface is defined by the cylindrical surface of the major bore.

35. A motor or pump according to claim 15, wherein coupling means is drivably connected to said main gear and is 12 movement of said main gear relative to the housing is restricted by a single-bearing surface, and said bearing surface is defined by the cylindrical surface of the major bore.

38. A motor or pump according to claim 32, wherein lateral movement of said main gear relative to the housing is restricted by a singlebearing surface, and said bearing surface is defined by the cylindrical surface of the major bore. 

1. A fluid motor or pump of the gear type including, a housing having a major bore and at least two minor bores formed therein, the axes of the bores being substantially parallel and being relatively disposed so that said bores communicate, a main gear rotatably mounted within said major bore, and arranged so that lateral movement thereof relative to said housing is restricted by a single-bearing surface, said bearing surface being defined by the cylindrical surface of said major bore, a pinion gear rotatably mounted within each said minor bore and meshing with the main gear, a pair of fluid manifolds formed in said housing and respectively communicating with said minor bore, and coupling means drivably connected to said main gear and being drivably connectable to a rotatable driving or driven member, said coupling means allowing misalignment of the respective rotational axes of said main gear and said driving or driven member.
 2. A motor or pump according to claim 1, wherein said coupling means includes a quill gear rotatably mounted within said housing, one axial end portion of the quill gear being in driving engagement with said main gear, and the opposite axial end portion being operatively connectable to the driving or driven member.
 3. A motor or pump according to claim 2, wherein said quill gear is provided with a set of external teeth and a set of internal teeth, said external and internal sets being spaced apart in the axial direction of the quill gear, said main gear having a set of internal teeth which are substantially complementary to and engage with the external teeth of the quill, and the internal teeth of the quill are engageable with substantially complementary teeth formed on said driving or driven member.
 4. A motor or pump according to claim 1, wherein a plurality of said minor bores are provided in equally spaced relationship about the circumference of said major bore, and one of said pinions is located within each of said minor bores.
 5. A motor or pump of the gear type including, a housing having a major bore and a minor bore formed therein, the axes of the two bores being substantially parallel and being relatively disposed so that said bores communicate, a main gear rotatably mounted within said major bore, a pinion gear rotatably mounted within said minor bore and meshing with the main gear, a pair of fluid manifolds formed in said housing and respectively communicating with said minor bore, coupling means drivably connected to said main gear and being drivably connectable to a rotatable driving or driven member, said coupling means allowing misalignment of the respective rotational axes of said main gear and said driving or driven member, a pressure compensating chamber in the form of a continuous band formed within said housing and surrounding said major and minor bores, said chamber being elongated in the axial direction of said bores and being relatively thin in a direction radially of said major bore, and means allowing passage of working fluid to said chamber to pressurize same and thereby minimize radially outward deflection of the housing part or parts surrounding said bores.
 6. A motor or pump according to claim 5, wherein said housing includes an intermediate part defining the cylindrical surfaces of both said bores, and two end parts releasably secured to the intermediate part to form opposite end walls respectively of said bores; and a cylindrical band surrounds and engages a cylindrical outer surface of said intermediate part, the inner surface of said band also engaging a respective cylindrical surface of each of said end parts, an outer compensating member surrounding said band and engaging at least part of tHe outer cylindrical surface thereof, said compensating means being defined between adjacent cylindrical surfaces of the band and the outer compensating member, and passage means formed within said housing connecting said chamber to at least one of said fluid manifolds.
 7. A motor or pump according to claim 6, wherein said passage means is arranged to connect the chamber to both said manifolds, and a valve is provided in said passage means to automatically disconnect the chamber from the manifold which is subjected to the lower fluid pressure and connect the chamber to the manifold which is subjected to the higher fluid pressure.
 8. A motor or pump according to claim 5, wherein said coupling means includes a quill gear rotatably mounted within said housing, one axial end portion of the quill gear being in driving engagement with said main gear, and the opposite axial end portion being operatively connectable to the driving or driven member.
 9. A motor or pump according to claim 5, wherein a plurality of said minor bores are provided in equally spaced relationship about the circumference of said major bore, and one of said pinions is located within each of said minor bores.
 10. A fluid motor or pump of the gear type including, a housing having a major bore and a minor bore formed therein, the axes of the two bores being substantially parallel and being relatively disposed so that said bores communicate, said housing being formed as two parts which are assembled in face to face relationship along a plane extending normal to the axes of said bores and located substantially midway in the axial length of the major bore, said major bore being defined by a pair of complementary pockets each of which is formed in a respective one of said housing parts, said minor bore extending through at least one end face of the housing remote from said plane, a seal cap removably mounted within said minor bore adjacent the or each said end face through which it extends, a main gear rotatably mounted within said major bore, a pinion gear rotatably mounted within said minor bore and meshing with the main gear, a cylindrical bearing member secured to each end of the pinion gear against movement relative thereto, each said bearing member having substantially the same outside diameter as said pinion, a pair of fluid manifolds formed in said housing and respectively communicating with said minor bore, and coupling means drivably connected to said main gear and being drivably connectable to a rotatable driving or driven member, said coupling means allowing misalignment of the respective rotational axes of said main gear and said driving or driven member.
 11. A motor or pump according to claim 10, wherein said pinion and the associated cylindrical bearing members are rotatably and slidably mounted within said minor bore, and said pinion is retained against substantial axial movement by intermeshing teeth of the main gear located between and engageable with adjacent end faces of the bearing members.
 12. A motor or pump according to claim 11, wherein said manifolds are formed in the same part of the housing.
 13. A motor or pump according to claim 10, wherein said coupling means includes a quill gear rotatably mounted within said housing, one axial end portion of the quill gear being in driving engagement with said main gear, and the opposite axial end portion being operatively connectable to the driving or driven member.
 14. A motor or pump according to claim 10, wherein a plurality of said minor bores are provided in equally spaced relationship about the circumference of said major bore, and one of said pinions is located within each of said minor bores.
 15. A fluid motor or pump of the gear type including, a housing having a major bore and a minor bore formed therein, the axes of the two bores being substantially parallel and being relatively disposed so that said bores communicate, said housing being formed as two parts which are assembled in face to face relationship along a Plane extending normal to the axes of said bores and located substantially midway in the axial length of the major bore, said major bore being defined by a pair of complementary pockets each of which is formed in a respective one of said housing parts, said minor bore extending through at least one end face of the housing remote from said plane, a seal cap removably mounted within said minor bore adjacent the or each said end face through which it extends, a main gear rotatably mounted within said major bore, a pinion gear rotatably mounted within said minor bore and meshing with the main gear, a cylindrical bearing member secured to each end of the pinion gear against movement relative thereto, each said bearing member being coaxial with said pinion and having substantially the same outside diameter as said pinion, a pair of fluid manifolds formed in said housing and respectively communicating with said minor bore, and pressure-compensating means located radially outwards of said minor bore and arranged to minimize radially outward deflection of the housing part or parts surrounding the bores.
 16. A motor or pump according to claim 15, wherein said compensating means includes a cavity formed in said housing radially outwardly of said minor bore and communicating therewith through a communication passage.
 17. A motor or pump according to claim 16, wherein said cavity is elongated in the axial direction of the pinion, is in substantial radial alignment with said pinion and extends for substantially the full length thereof, and in transverse cross section is shaped as a narrow arcuate groove which generally follows the curvature of said minor bore.
 18. A motor or pump according to claim 16, wherein a plurality of said cavities are located side by side adjacent said minor bore.
 19. A motor or pump according to claim 16, wherein said pinion and the associated cylindrical bearing members are rotatably and slidably mounted within said minor bore, and said pinion is retained against substantial axial movement by intermeshing teeth of the main gear located between and engageable with adjacent end faces of the bearing members.
 20. A motor or pump according to claim 16, wherein said coupling means includes a quill gear rotatably mounted within said housing, one axial end portion of the quill gear being in driving engagement with said main gear, and the opposite axial end portion being operatively connectable to the driving or driven member.
 21. A motor or pump according to claim 15, wherein said compensating means includes a cylindrical band at least partially contained within a recess formed in the radially outer surface of the housing, and feed means for feeding fluid under pressure into a space defined between the inner cylindrical surface of said band and the base of said recess.
 22. A motor or pump according to claim 21, wherein the inner cylindrical surface of said band and the base of the recesses are substantially complementary so that only a film of fluid is receivable within said space.
 23. A motor or pump according to claim 21, wherein said space is communicable with both said manifolds through said feed means, and said feed means includes a valve mechanism operable to automatically communicate the space with the manifold subjected to the higher pressure and prevent communication between the space and the manifold subjected to the lower pressure.
 24. A motor or pump according to claim 21, wherein said pinion and the associated cylindrical bearing members are rotatably and slidably mounted within said minor bore, and said pinion is retained against substantial axial movement by intermeshing teeth of the main gear located between and engageable with adjacent end faces of the bearing members.
 25. A motor or pump according to claim 15, wherein a plurality of said minor bores are provided in equally spaced relationship about the circumference of said major bore, and one of said pinions is located within each of said minor bores.
 26. A motor or puMp according to claim 21, wherein coupling means is drivably connected to said main gear and is drivably connectable to a rotatable driving or driven member so as to allow misalignment of the respective rotational axes of said main gear and said driving or driven member said coupling means includes a quill gear rotatably mounted within said housing, one axial end portion of the quill gear being in driving engagement with said main gear, and the opposite axial end portion being operatively connectable to the driving or driven member.
 27. A motor or pump according to claim 5, wherein said housing includes, an outer casing having a skirt portion defining a cylindrical bore and an end wall closing one end of said skirt bore, an intermediate part contained within said skirt bore and defining the cylindrical surfaces of both the major and minor bores, two end parts also contained within said skirt bore and disposed on opposite sides respectively of the intermediate part to form end walls of said major and minor bores, and a retainer plate releasably locked within the open end of the skirt bore so as to restrict axial movement of the housing parts interposed between it and the end wall of the casing.
 28. A motor or pump according to claim 27, wherein the intermediate and end parts of the housing each has a cylindrical outer surface of substantially the same diameter, and a cylindrical band disposed about said housing parts and engaging the outer cylindrical surfaces thereof, said compensating chamber being defined between the outer cylindrical surface of said band and the adjacent surface of the skirt bore.
 29. A motor or pump according to claim 28, wherein the outer cylindrical surface of the band is substantially complementary to the adjacent skirt bore surface so that only a film of fluid is receivable between those surfaces, and fluid is conveyed to said space from the major and minor bores by passing between the adjacent surfaces of said retainer plate and adjacent housing end part and the casing end wall and adjacent housing end part respectively.
 30. A motor or pump according to claim 28, wherein the outer cylindrical surface of the intermediate housing part is grooved to allow limited radially inward deflection of said cylindrical band.
 31. A motor or pump according to claim 30, wherein said grooved surface of the intermediate housing part communicates with atmosphere.
 32. A motor or pump according to claim 27, wherein a plurality of said minor bores are provided in equally spaced relationship about the circumference of said major bore, and one of said pinions is located within each of said minor bores.
 33. A motor or pump according to claim 9, wherein lateral movement of said main gear relative to the housing is restricted by a single-bearing surface, and said bearing surface is defined by the cylindrical surface of the major bore.
 34. A motor or pump according to claim 14, wherein lateral movement of said main gear relative to the housing is restricted by a single-bearing surface, and said bearing surface is defined by the cylindrical surface of the major bore.
 35. A motor or pump according to claim 15, wherein coupling means is drivably connected to said main gear and is drivably connectable to a rotatable driving or driven member so as to allow misalignment of the respective rotational axes of said main gear and said driving or driven member.
 36. A motor or pump according to claim 14, wherein lateral movement of said main gear relative to the housing is restricted by a single-bearing surface, and said bearing surface is defined by the cylindrical surface of the major bore.
 37. A motor or pump according to claim 25, wherein lateral movement of said main gear relative to the housing is restricted by a single-bearing surface, and said bearing surface is defined by the cylindrical surface of the major bore.
 38. A motor or pump according to claim 32, wherein lateral movement of said main gear relative to the housing is restricted by a single-bearIng surface, and said bearing surface is defined by the cylindrical surface of the major bore. 